Riser tensioner having an emergency seal

ABSTRACT

A riser tensioner has an emergency seal and tensions a riser extending to the seabed from a drilling ship which drills for submarine resources such as oil. The riser tensioner is disposed under a drilling ship to tension a riser used for drilling operation of submarine resources and including a plurality of cylinders into which oil is supplied. The riser tensioner further includes a piston rod partially inserted into each of the cylinders and reciprocating within the cylinder, a piston seal disposed between a head of the piston rod and a wall of the cylinder to provide fluid sealing therebetween; an oil leakage detector detecting oil leakage through the piston seal, and an emergency seal disposed in a groove formed at an upper portion of the head of the piston rod to be compressed towards the wall of the cylinder and protrude from the head of the piston rod to prevent oil leakage through the wall of the cylinder when the oil leakage detector detects oil leakage.

BACKGROUND

1. Technical Field

The present disclosure relates to a riser tensioner having an emergency seal. More particularly, the present disclosure relates to a riser tensioner that includes an emergency seal and tensions a riser extending to the seabed from a drilling ship which drills for submarine resources such as oil.

2. Description of the Related Art

Currently, with rapid industrialization and development of technology, stable production and supply of resources such as oil has become a crucial global issue due to increase in use of such resources.

For this reason, development of marginal fields or deep-sea oilfields, which have been ignored due to their low economic feasibility, has become economically feasible. Thus, offshore drilling vessels suitable for seabed oilfields have been developed together with seabed drilling technology.

Conventionally, submarine drilling is performed using submarine drilling rig ships or stationary platforms, which can sail only with assistance of tugboats and are anchored at one point at sea using moorings during drilling operation. Recently, submarine drilling is performed using a drillship which is fitted with advanced drilling apparatuses and has the same shape as a general ship so as to sail by its own power.

A rig ship or drillship (hereinafter, referred to as a drilling ship) fitted with a variety of drilling apparatuses to drill for oil or gas under the seabed is formed at the center thereof with a moon pool through which a riser or a drill pipe can move vertically for drilling operation.

FIG. 1 is a side view of a conventional drilling ship floating on a sea surface for drilling operation.

A worker advances a riser 4 and a drill pipe 5 downwards through a moon pool 3 formed at the center of a drilling ship 1 using a lifting device provided to a derrick 2 to drill for submarine resources stored in an oil well 13 at bedrock 12 under the seabed 6.

The riser 4 is advanced to the seabed 6 to provide a path through which mud returns, prior to advancing the drill pipe 5 to the oil well 13. With the riser 4 installed between the drilling ship and the seabed, the drill pipe 5 is advanced downwards inside the riser 4 to the oil well 13 through a sea bottom stratum 11.

As such, when the riser 4 is advanced downwards to the seabed 6 or the drill pipe 5 is advanced to the oil well 13, short riser members of the riser or pipe members of the drill pipe 5 connected to each other are advanced downwards instead of using long riser members or drill pipe members connected to each other. On the seabed 6, a blowout preventer (BOP) 7 is installed to prevent high pressure from being transferred upwards along the drill pipe 5. In the sea bottom stratum 11, a casing 8 is secured by cement and a drill pipe 5 fitted with a drill bit 10 is inserted into the casing 8 to drill for submarine resources. To prevent the drill bit 10 from being excessively heated by heat generated by drilling operation of the drill bit 10 into the sea bottom stratum while facilitating the drilling operation through lubrication, mud 9 is inserted into the drill pipe 5. Then, the mud is discharged through the drill bit 10 and returns through the casing 8 and the riser 4. When drilling is completed, the drill pipe 5 is transferred to a drill floor through the moon pool 3, followed by disassembly for transportation to a storage location.

FIG. 2 is an enlarged view of Part A in FIG. 1.

The riser 4 may be divided into an upper riser 4 a and a lower riser 4 b with respect to a slip joint 20. Although the riser 4 extends from the drilling ship to the sea bottom, the slip joint 20 is provided to the middle of the riser 4 to allow the upper and lower risers 4 a, 4 b to move vertically with respect to each other in order to prevent vibration from being directly transferred from the upper riser 4 a connected to the drilling ship to the lower riser 4 b due to waves.

Since the distance of the riser 4 from the drilling ship to the sea bottom is several thousand meters and the mud passes through the riser 4, the total weight of the riser 4, the mud inside the riser and the BOP approaches several tons.

When the drilling ship is moved by waves and force generated due to movement of the upper riser 4 a connected to the drilling ship is directly transferred to the lower riser 4 b, the riser 4 having a length of several thousand meters may undergo buckling. To prevent such a phenomenon, the drilling ship is provided with the slip joint 20 and a riser tensioner. The riser tensioner tensions the lower riser 4 b with a predetermined tensile force, thereby minimizing influence of movement of the drilling ship by waves on the riser 4.

The riser tensioner generally includes a support ring 30, a cylinder device 40, and a hydraulic device 50.

The support ring 30 connects the slip joint 20 to the cylinder device 40. The cylinder device 40 includes a cylinder 41 connected to the drilling ship and a piston rod 42 connected to the support ring 30. Generally, a plurality of cylinder devices 40 is arranged along the circumference of the riser 4. The hydraulic device 50 supplies hydraulic pressure to each of the cylinders 41 to raise the piston rod 42, so that the lower riser 4 b connected to the slip joint 20 is tensioned.

The hydraulic device 50 includes an accumulator 51 and a pneumatic container 52. When air is supplied from the pneumatic container 52 to the accumulator 51, oil is supplied into the cylinder 41 by pressure of the air, thereby lifting the piston rod 42.

In the case where the distance between the cylinder 41 and the piston rod 42 is changed due to vertical movement of the drilling ship by waves, hydraulic pressure supplied to the cylinder 41 by the hydraulic device is controlled to be constant to pull the lower riser 4 b by constant tensile force.

FIG. 3 is a cross-sectional view of a cylinder of a conventional riser tensioner.

A piston seal 43 is disposed between the cylinder 41 and a head 42 a of the piston rod 42 to prevent oil supplied to a lower portion “b” of the cylinder 41 by a hydraulic system from leaking to an upper portion “a” of the cylinder 41 while the piston rod 42 is tensioned.

Since offshore drilling is performed for a long duration, there is a high possibility of oil leakage when the piston seal 43 is worn by reciprocation of the piston rod 42. The leaked oil is gathered in the upper portion of the cylinder 41 above the head 42 a of the piston rod 42. Then, when the amount of leaked oil increases over time and the stroke of the piston rod 42 increases by high waves, the oil gathered in the upper portion “a” of the piston rod 42 imparts compressive force to the piton rod 42 and causes the piston rod 42 to bend when the piston rod 42 moves towards an upper dead point.

Since the riser tensioner is located under the drilling ship, it is usually very difficult to detect oil leakage. Further, since the cylinder is dissembled from under the drilling ship to repair the cylinder in the event of oil leakage from the cylinder, the conventional riser tensioner has a problem in that it takes a long time to repair the cylinder. Moreover, when the riser tension is not properly operated due to excessive oil leakage, there is a high possibility of a large accident such as riser buckling and the like.

Therefore, there is a need for a detector capable of detecting oil leakage when oil leaks to the upper portion “a” of the cylinder 41 due to abrasion of a piston seal 43.

Further, there is a need for a mechanism for replacing the abraded piston seal 43 without dissembling the cylinder 41 when oil leaks to the upper portion “a” of the cylinder due to abrasion of the piston seal 43.

A riser tensioner disclosed in U.S. Pat. No. 7,112,011 (issue date: Sep. 26, 2006) includes a typical seal unit and has very low efficiency of blocking oil leakage due to the absence of a mechanism capable of preventing oil leakage based on detection of the oil leakage by the seal unit of a piston rod.

BRIEF SUMMARY

The present disclosure is directed to solving the problems of the related art as described above, and an embodiment of the present disclosure provides a riser tensioner that includes a detector capable of detecting oil leakage due to abrasion of a piston seal disposed between a cylinder and a piston rod, and an emergency seal capable of replacing the abraded piston seal.

In accordance with one aspect of the present disclosure, there is provided a riser tensioner disposed under a drilling ship to tension a riser used for drilling operation of submarine resources and including a plurality of cylinders into which oil is supplied. The riser tensioner further includes: a piston rod partially inserted into each of the cylinders and reciprocating within the cylinder; a piston seal disposed between a head of the piston rod and a wall of the cylinder to provide fluid sealing therebetween; an oil leakage detector detecting oil leakage through the piston seal; and an emergency seal disposed in a groove formed at an upper portion of the head of the piston rod to be compressed towards the wall of the cylinder and protrude from the head of the piston rod to prevent oil leakage through the wall of the cylinder when the oil leakage detector detects the oil leakage.

The emergency seal may be attached to the upper portion of the head of the piston rod by a fastening member.

The emergency seal may be guided by a seal guide attached to the upper portion of the head of the piston by the fastening member.

In accordance with another aspect of the present disclosure, there is provided a riser tensioner disposed under a drilling ship to tension a riser used for drilling operation of submarine resources and including a plurality of cylinders into which oil is supplied. The riser tensioner further includes: a piston rod partially inserted into each of the cylinders and reciprocating within the cylinder; a piston seal disposed between a head of the piston rod and a wall of the cylinder to provide fluid sealing therebetween; an oil leakage detector detecting oil leakage through the piston seal; and an emergency seal disposed in the head of the piston rod to protrude from the head of the piston rod to provide fluid sealing between the cylinder and the piston rod when the oil leakage is detected by the oil leakage detector.

The head of the piston rod may have a groove formed on a surface thereof, and the emergency seal may be compressed by hydraulic pressure to protrude from the head of the piston rod through the groove.

The riser tensioner may further include an actuator that compresses the emergency seal.

The actuator may include a fluid passage extending to the emergency seal through the piston rod, and an oil valve supplying oil into the fluid passage. Here, the oil valve is opened to transfer hydraulic pressure to the emergency seal through the fluid passage when oil leakage is detected by the oil leakage detector.

The piston rod may be formed with a collection passage through which the leaked oil passes, and the riser tensioner may further include a collection tank connected to the collection passage of the piston rod. Here, the oil leakage detector determines the oil leakage based on a detection result of an amount of oil collected in the collection tank.

As such, the riser tensioner according to the present disclosure includes the oil leakage detector for detecting oil leakage through the piston seal, and the emergency seal configured to protrude from the head of the piston rod or to be compressed towards the wall of the cylinder to provide fluid sealing instead of the piston seal upon emergency, such as oil leakage due to abrasion of the piston seal, thereby preventing oil leakage towards the upper portion of the cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a conventional drilling ship floating on a sea surface for drilling operation;

FIG. 2 is an enlarged view of Part A in FIG. 1;

FIG. 3 is a schematic sectional view of a cylinder of a conventional riser tensioner;

FIG. 4 is a sectional view of a riser tensioner in accordance with one embodiment of the present disclosure;

FIG. 5 is a sectional view of the riser tensioner of FIG. 4, illustrating an emergency seal protruding from a head of a piston rod;

FIG. 6 is a sectional view of an oil leakage detector of a riser tensioner in accordance with another embodiment of the present disclosure;

FIG. 7 is a sectional view of a riser tensioner in accordance with a further embodiment of the present disclosure; and

FIG. 8 is a sectional view of the riser tensioner of FIG. 7, illustrating operation of an emergency seal upon oil leakage.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Herein, like elements will be denoted by like reference numerals throughout the accompany drawings.

FIG. 4 is a sectional view of a riser tensioner in accordance with one embodiment of the present disclosure. FIG. 5 is a sectional view of the riser tensioner of FIG. 4, illustrating an emergency seal protruding from a head of a piston rod. FIG. 6 is a sectional view of an oil leakage detector of a riser tensioner in accordance with another embodiment of the present disclosure.

Generally, a riser tensioner refers to a device that is connected to a drilling ship to tension a riser in order to prevent the riser from buckling upon movement of the drilling ship by waves during drilling for submarine resources. Herein, the drilling ship means any kind of offshore floating structure for drilling of submarine resource, such as drill ships, rigs, semi-submersible rigs, tension leg platforms, and the like .

A riser tensioner 100 according to one embodiment is also configured to tension the riser by allowing a piston rod 120 to be pulled by hydraulic pressure supplied to a cylinder 110. Operation of fluid inside the cylinder 110 of the riser tensioner 100 is the same or similar to that of the related art, and a detailed description thereof will thus be omitted.

The riser tensioner 100 includes the cylinder 110, the piston rod 120, a piston seal 130, an oil leakage detector, an emergency seal 150, an oil valve 170, and the like.

Oil is introduced into the cylinder 110 and generates hydraulic pressure to raise the piston rod 120 in a direction indicated by an arrow.

The piston rod 120 is partially inserted into the cylinder 110 to reciprocate within the cylinder 110 by hydraulic pressure inside the cylinder 110 or by movement of the drilling ship due to waves. The piston rod 120 has a T shape and is provided at an upper portion thereof with a head 120 a.

The piston seal 130 is disposed between the head 120 a of the piston rod 120 and a wall of the cylinder 110 to provide hydraulic sealing and restrict movement of the oil flowing into the cylinder 110, so that hydraulic pressure is generated in the cylinder 110.

Since offshore drilling is performed for a long duration, oil can leak through the piston seal 130 in the case where the piston seal 130 is worn out due to continuous reciprocation of the piston rod 120. The leaked oil is gathered in an upper portion of the cylinder 110 above the head 120 a of the piston rod 120. Then, the amount of leaked oil increases over time and the oil gathered in the upper portion of the piston rod imparts compressive force to the piston rod 120 when the piston rod 42 moves towards an upper dead point, causing negative influence on reciprocation of the piston rod 120.

Thus, in this embodiment, the riser tensioner includes the oil leakage detector for detecting oil leaked into the upper portion of the cylinder 110 and the emergency seal 150 which may provide a function of the piston seal 130 when the piston seal 130 is abraded.

The oil leakage detector may include a controller that determines oil leakage based on a difference between the amount of oil introduced into the cylinder 110 and the amount of oil remaining in the cylinder 110. The amount of oil introduced into the cylinder 110 is obtained by subtracting the amount of oil remaining in another part such as an accumulator 51 (see FIG. 2) except for the cylinder 110 from the total input amount of oil. The actual amount of oil remaining in the cylinder 110 is measured by a load sensor or the like disposed inside the cylinder 110. Considering that a minute amount of oil can leak through the piston seal 130, it is determined that oil leakage occurs when the amount of leaked oil is a predetermined amount or more.

Alternatively, the oil leakage detector may determine oil leakage based on the amount of oil gathered in a collection tank 190, when the oil leaked through a collection passage 180 formed in the piston rod 120 is gathered in a collection tank 190 through a connection passage 181. The collection tank 190 may be located at any proper place. The collection tank 190 may be provided with a sensor 195 which detects the amount of leaked oil (see FIG. 6). The oil leakage detector may be realized in various ways by those skilled in the art so long as it can detect oil leakage.

When oil leakage is detected by the oil leakage detector, an actuator compresses the emergency seal 150 such that the emergency seal 150 protrudes from the head 120 a of the piston rod 120.

The actuator may be realized in various ways. For example, the actuator includes a fluid passage 160 extending to the emergency seal 150 through the piston rod 120, and an oil valve 170 supplying oil into the oil passage 160.

When oil leakage is detected, the oil leakage detector outputs an oil leakage signal to a controller (not shown), which in turn opens the oil valve 170. The oil valve 170 is connected to an oil operation pump 171 connected to an HPU, such that when the oil valve 170 is opened, oil is supplied from the oil operation pump 171 to transfer hydraulic pressure to the emergency seal 150 along the oil passage 160.

The head 120 a of the piston rod 120 is formed with a ring-shaped groove 121 along the circumference of the head 120 a, and the emergency seal 150 is usually maintained in a compressed state within the groove 121 on an inner side of the head 120 a of the piston rod 120. In one embodiment, the emergency seal 150 includes a rounded distal end 150 a and a proximal end 150 b for maintaining a protruded state of the distal end 150 a when the distal end 150 a protrudes from the head 120 a of the piston rod 120. The shape and structure of the emergency seal 150 may be realized in various ways by those skilled in the art.

When the hydraulic pressure is transferred to the emergency seal 150 through detection of oil leakage, the emergency seal 150 is compressed such that the distal end of the emergency seal 150 protrudes from the groove 121, as shown in FIG. 5. At this time, the proximal end 150 b of the emergency seal 150 is supported by an inner wall of the head 120 a of the piston rod 120, thereby enabling hydraulic sealing to be achieved while maintaining the emergency seal 150 in the protruded state.

FIG. 7 is a sectional view of a riser tensioner in accordance with a further embodiment of the present disclosure. FIG. 8 is a sectional view of the riser tensioner of FIG. 7, illustrating operation of an emergency seal upon oil leakage.

For a riser tensioner 200 according to this embodiment, an emergency seal 250 is guided in operation by a seal guide 251 which is attached to an upper side of a head 220 a of a piston rod 220 by a fastening member 252 such as a bolt and the like. Alternatively, the emergency seal 250 may be operated in a state of being attached to the upper side of the head 220 a of the piston rod 220 by the fastening member 252 such as a bolt, instead of being guided by the seal guide 251.

When oil leakage due to abrasion of the piston seal 230 is detected by an oil leakage detector, the actuator compresses the emergency seal 250 towards a wall of the cylinder 210 such that the emergency seal 250 acts as an assistant seal. The oil leakage detector has substantially the same structure as that of the oil leakage detector described with reference to FIGS. 4 and 5.

As in the embodiment of FIG. 4, the actuator may include a fluid passage 260 extending to the emergency seal 250 through the piston rod 220, and an oil valve 270 supplying oil into the oil passage 260.

When oil leakage is detected, the oil leakage detector outputs an oil leakage signal to a controller (not shown), which in turn opens the oil valve 270. The oil valve 270 is connected to an oil operation pump 271 connected to an HPU, such that when the oil valve 270 is opened, oil is supplied from the oil operation pump 271 to transfer hydraulic pressure to the emergency seal 250 along the oil passage 260. Such hydraulic pressure compresses the emergency seal 250 to be brought into close contact with a wall of the cylinder 210, thereby allowing the emergency seal 250 to act as an assistant seal.

According to this embodiment, since the emergency seal 250 is attached to the upper side of the head 220 a of the piston rod 220, the emergency seal 250 may be easily installed, maintained or repaired in the case of failure.

As such, according to the embodiments, the riser tensioner includes the oil leakage detector for detecting oil leakage through the piston seal, and the emergency seal configured to protrude from the head of the piston rod or to be compressed towards the wall of the cylinder to provide fluid sealing instead of the piston seal upon emergency, such as oil leakage due to abrasion of the piston seal, thereby preventing oil leakage towards the upper portion of the cylinder.

Generally, considering that the riser tensioner is located under a drilling ship, causing a difficulty in approaching the riser tensioner and that repair of the riser tensioner requires long time, the riser tensioner including the oil leakage detector and the emergency seal according to the embodiments serves as a sufficient safety mechanism in emergency.

In the riser tensioner according to the embodiments of the present disclosure, it is apparent to those skilled in the art that the oil leakage detector, the emergency seal and the actuator may be realized in various ways.

The embodiment described above can be combined to provide further embodiments. All of the patents, patent application publications, patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiment can be modified, if necessary, to employ concepts of the various patents, applications and publications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed as limiting the claims to the specific embodiments disclosed in the specification and the claims, but should be construed as including all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure. 

1. A riser tensioner disposed under a drilling ship to tension a riser used for drilling operation of submarine resources and including a plurality of cylinders into which oil is supplied, the riser tensioner further comprising: a piston rod partially inserted into each of the cylinders and reciprocating within the cylinder; a piston seal disposed between a head of the piston rod and a wall of the cylinder to provide fluid sealing therebetween; an oil leakage detector detecting oil leakage through the piston seal; and an emergency seal disposed in a groove formed at an upper portion of the head of the piston rod to be compressed towards the wall of the cylinder and protrude from the head of the piston rod to prevent oil leakage through the wall of the cylinder when the oil leakage detector detects oil leakage.
 2. The riser tensioner of claim 1, wherein the emergency seal is attached to the upper portion of the head of the piston rod by a fastening member.
 3. The riser tensioner of claim 1, wherein the emergency seal is guided by a seal guide attached to the upper portion of the head of the piston by the fastening member.
 4. A riser tensioner disposed under a drilling ship to tension a riser used for drilling operation of submarine resources and including a plurality of cylinders into which oil is supplied, the riser tensioner further comprising: a piston rod partially inserted into each of the cylinders and reciprocating within the cylinder; a piston seal disposed between a head of the piston rod and a wall of the cylinder to provide fluid sealing therebetween; an oil leakage detector detecting oil leakage through the piston seal; and an emergency seal disposed in the head of the piston rod to protrude from the head of the piston rod to provide fluid sealing between the cylinder and the piston rod when oil leakage is detected by the oil leakage detector.
 5. The riser tensioner of claim 4, wherein the head of the piston rod has a groove formed on a surface thereof, and the emergency seal is compressed by hydraulic pressure to protrude from the head of the piston rod through the groove.
 6. The riser tensioner of claim 1, further comprising: an actuator that compresses the emergency seal.
 7. The riser tensioner of claim 6, wherein the actuator comprises a fluid passage extending to the emergency seal through the piston rod, and an oil valve supplying oil into the fluid passage, the oil valve being opened to transfer hydraulic pressure to the emergency seal through the fluid passage when oil leakage is detected by the oil leakage detector.
 8. The riser tensioner of claim 1, further comprising: a collection tank connected to a collection passage of the piston rod, through which leaked oil passes, the oil leakage detector determining the oil leakage based on a detection result of an amount of oil collected in the collection tank. 